Abstract:

A lighting control circuit comprises a dimming level detection circuit, a
waveform generator and a comparator circuit. The dimming level detection
circuit is configurable to generate a first voltage level signal
corresponding to a selected one of at least two different types of
dimming signals selected from among an AC phase cut dimming signal, a DC
voltage level dimming signal or a PWM dimming signal. The waveform
generator is configured to output a periodic waveform. The comparator
circuit is configured to compare the periodic waveform with the first
voltage level signal to generate an output waveform having a duty cycle
corresponding to a dimming level of the one of the at least two different
input dimming signals and a frequency corresponding to the frequency of
the periodic waveform. Also, methods of controlling lighting.

Claims:

1. A lighting control circuit comprising:a dimming level detection circuit
configurable to generate a first voltage level signal corresponding to a
selected one of at least two different types of dimming signals, the
types of dimming signals comprising at least two of an alternating
current (AC) phase cut dimming signal, a direct current (DC) voltage
level dimming signal or a pulse-width modulated (PWM) dimming signal;a
waveform generator configured to output a waveform generator periodic
waveform; anda comparator circuit configured to compare the waveform
generator periodic waveform with the first voltage level signal to
generate a comparator waveform having a comparator duty cycle
corresponding to a dimming level of the one of the at least two different
input dimming signals and a frequency corresponding to a frequency of the
waveform generator periodic waveform.

2. A lighting control circuit as recited in claim 1, wherein the dimming
level detection circuit is user configurable to generate the voltage
level from one of the at least two different input dimming signals.

3. A lighting control circuit as recited in claim 1, wherein the dimming
level detection circuit is preconfigured to generate the voltage level
from one of the at least two different input dimming signals.

4. A lighting control circuit as recited in claim 1, wherein the dimming
level detection circuit is configurable by electrical jumper
configuration.

5. A lighting control circuit as recited in claim 1, wherein the dimming
level detection circuit is configurable by component selection.

6. A lighting control circuit as recited in claim 1, wherein the dimming
level detection circuit is configurable by connection to different input
connectors associated with the at least two different types of dimming
signals.

7. A lighting control circuit as recited in claim 1, wherein the lighting
control circuit further comprises a shutdown comparator circuit which is
configured to compare the first voltage level signal with a shutdown
threshold voltage and to generate a shutdown signal based on the
comparison.

8. A lighting control circuit as recited in claim 1, wherein the dimming
level detection circuit comprises a wired OR circuit of voltage levels
corresponding to the at least two different types of dimming signals.

9. A lighting control circuit as recited in claim 1, wherein the dimming
level detection circuit comprises a duty cycle detection circuit and an
averaging circuit.

10. A lighting control circuit as recited in claim 9, wherein the
averaging circuit comprises a first averaging circuit configured to
average a detected duty cycle of an AC dimming signal and a second
averaging circuit configured to average a duty cycle of a PWM dimming
signal.

11. A lighting control circuit comprising:means for generating a first
voltage level signal corresponding to a selected one of at least two
different types of dimming signals, the types of dimming signals
comprising at least two of an alternating current (AC) phase cut dimming
signal, a direct current (DC) voltage level dimming signal or a
pulse-width modulated (PWM) dimming signal;means for generating a
waveform generator periodic waveform; andmeans for comparing the waveform
generator periodic waveform with the first voltage level signal to
generate a comparator waveform having a comparator duty cycle
corresponding to a dimming level of the selected one of at least two
different types of dimming signals and a frequency corresponding to a
frequency of the waveform generator periodic waveform.

12. A lighting control circuit as recited in claim 11, wherein the
lighting control circuit further comprises means for comparing the first
voltage level signal with a shutdown threshold voltage and generating a
shutdown signal based on the comparison.

13. A method of controlling lighting, comprising:generating a first
voltage level signal based on a selected one of at least two different
types of dimming signals, the types of dimming signals comprising at
least two of an alternating current (AC) phase cut dimming signal, a
direct current (DC) voltage level dimming signal or a pulse-width
modulated (PWM) dimming signal;generating a waveform generator periodic
waveform; andcomparing the waveform generator periodic waveform with the
first voltage level signal to generate a comparator waveform having a
comparator duty cycle corresponding to a dimming level of the one of the
at least two different input dimming signals and a frequency
corresponding to a frequency of the waveform generator periodic waveform.

14. A method as recited in claim 13, further comprising:obtaining user
input to identify the selected one of at least two different types of
dimming signals.

15. A method as recited in claim 13, further comprising preconfiguring the
selected one of the at least two different input dimming signals.

16. A method as recited in claim 13, further comprising setting an
electrical jumper to identify the selected one of at least two different
types of dimming signals.

17. A method as recited in claim 13, further comprising selecting
components for a voltage generation circuit based on the selected one of
at least two different types of dimming signals.

18. A method as recited in claim 13, wherein generating a first voltage
level comprises generating a first voltage level based on a presence of a
connection to different input connectors associated with the at least two
different types of dimming signals.

19. A method as recited in claim 13, further comprising comparing the
first voltage level signal with a shutdown threshold voltage and
generating a shutdown signal based on the comparison.

20. A method as recited in claim 13, wherein voltage levels corresponding
to the at least two different types of dimming signals are logically OR
wired.

21. A method as recited in claim 13, wherein generating a first voltage
level comprises:if the selected one of the at least two different dimming
signals comprises AC dimming:detecting the duty cycle of the detected AC
dimming signal; andaveraging the detected duty cycle of the AC dimming
signal to provide the first voltage level; andif the selected one of the
at least two different dimming signals comprises PWM dimming, averaging
the PWM dimming signal to provide the first voltage level.

22. A lighting device comprising:at least one solid state light emitter;a
lighting control circuit as recited in claim 1; anda driver circuit
configured to vary the intensity of output of the at least one solid
state light emitter in response to the comparator waveform.

23. A lighting device comprising:at least one solid state light emitter;a
lighting control circuit as recited in claim 1; andmeans for varying the
intensity of output of the at least one solid state light emitter in
response to the comparator waveform.

24. A lighting control circuit comprising:a dimming level detection
circuit,a waveform generator; anda comparator circuit,the dimming level
detection circuit being configured to generate voltage level signals
based on received input dimming signals of at least two types selected
from among (1) phase cut AC type dimming signals, (2) voltage level type
dimming signals and (3) PWM type dimming signals,the waveform generator
being configured to output a waveform generator periodic waveform, andthe
comparator circuit being configured to generate a comparator waveform
having (a) a comparator duty cycle based on a proportion of time during
which an instantaneous voltage of the voltage level signals exceeds an
instantaneous voltage level of the waveform generator periodic waveform,
and (b) a frequency corresponding to a frequency of the waveform
generator periodic waveform.

30. A lighting control circuit as recited in claim 24, wherein the duty
cycle of the comparator waveform generated by the comparator circuit is
proportional to a proportion of time during which the instantaneous
voltage of the voltage level signals exceeds the instantaneous voltage
level of the waveform generator periodic waveform.

31. A lighting control circuit as recited in claim 24, wherein the duty
cycle of the comparator waveform generated by the comparator circuit is
inversely proportional to a proportion of time during which the
instantaneous voltage of the voltage level signals exceeds the
instantaneous voltage level of the waveform generator periodic waveform.

[0002]The present application is related to U.S. patent application Ser.
No. ______, entitled "Frequency Converted Dimming Signal Generation"
filed concurrently herewith, the disclosure of which is incorporated
herein as if set forth in its entirety.

FIELD OF THE INVENTION(S)

[0003]The present inventive subject matter relates to lighting devices and
more particularly to power control for light emitting devices in the
presence of a dimming signal.

BACKGROUND OF THE INVENTION(S)

[0004]Many control circuits for lighting utilize phase cut dimming. In
phase cut dimming, the leading or trailing edge of the line voltage is
manipulated to reduce the RMS voltage provided to the light. When used
with incandescent lamps, this reduction in RMS voltage results in a
corresponding reduction in current and, therefore, a reduction in power
consumption and light output. As the RMS voltage decreases, the light
output from the incandescent lamp decreases.

[0005]An example of a cycle of a full wave rectified AC signal is provided
in FIG. 1A, a cycle of a phase cut rectified AC waveform is illustrated
in FIG. 1B and a cycle of a reverse phase cut AC waveform is illustrated
in FIG. 1C. As seen in FIGS. 1A through 1C, when phase cut dimming is
utilized, the duty cycle of the resulting rectified waveform is changed.
This change in duty cycle, if sufficiently large, is noticeable as a
decrease in light output from an incandescent lamp. The "off" time does
not result in flickering of the incandescent lamp because the filament of
an incandescent lamp has some thermal inertia and will remain at a
sufficient temperature to emit light even during the "off" time when no
current flows through the filament.

[0006]In addition to control of the AC signal, other techniques for
dimming light sources include 0-10V dimming and pulse width modulation
(PWM) dimming. In 0-10V and PWM dimming, a dimming signal separate from
the AC signal is provided to the light source. In 0-10V dimming, the
dimming signal is a voltage level between 0 and 10V DC. The light source
has a 100% output at 10V DC and a minimum output at 1V DC. Additional
details on 0-10V dimming can be found in IEC Standard 60929. 0-10V
dimming is conventionally used to dim fluorescent lighting.

[0007]In PWM dimming, a square wave is provided as the dimming signal. The
duty cycle of the square wave can be used to control the light output of
the light source. For example, with a 50% duty cycle, the output of the
light source may be dimmed 50%. With a 75% duty cycle, the light output
may be 75%. Thus, the light output of the light source may be
proportional to the duty cycle of the input square wave.

[0008]Recently, solid state lighting systems have been developed that
provide light for general illumination. These solid state lighting
systems utilize light emitting diodes or other solid state light sources
that are coupled to a power supply that receives the AC line voltage and
converts that voltage to a voltage and/or current suitable for driving
the solid state light emitters. Typical power supplies for light emitting
diode light sources include linear current regulated supplies and/or
pulse width modulated current and/or voltage regulated supplies.

[0009]Many different techniques have been described for driving solid
state light sources in many different applications, including, for
example, those described in U.S. Pat. No. 3,755,697 to Miller, U.S. Pat.
No. 5,345,167 to Hasegawa et al, U.S. Pat. No. 5,736,881 to Ortiz, U.S.
Pat. No. 6,150,771 to Perry, U.S. Pat. No. 6,329,760 to Bebenroth, U.S.
Pat. No. 6,873,203 to Latham, II et al, U.S. Pat. No. 5,151,679 to
Dimmick, U.S. Pat. No. 4,717,868 to Peterson, U.S. Pat. No. 5,175,528 to
Choi et al, U.S. Pat. No. 3,787,752 to Delay, U.S. Pat. No. 5,844,377 to
Anderson et al, U.S. Pat. No. 6,285,139 to Ghanem, U.S. Pat. No.
6,161,910 to Reisenauer et al, U.S. Pat. No. 4,090,189 to Fisler, U.S.
Pat. No. 6,636,003 to Rahm et al, U.S. Pat. No. 7,071,762 to Xu et al,
U.S. Pat. No. 6,400,101 to Biebl et al, U.S. Pat. No. 6,586,890 to Min et
al, U.S. Pat. No. 6,222,172 to Fossum et al, U.S. Pat. No. 5,912,568 to
Kiley, U.S. Pat. No. 6,836,081 to Swanson et al, U.S. Pat. No. 6,987,787
to Mick, U.S. Pat. No. 7,119,498 to Baldwin et al, U.S. Pat. No.
6,747,420 to Barth et al, U.S. Pat. No. 6,808,287 to Lebens et al, U.S.
Pat. No. 6,841,947 to Berg-johansen, U.S. Pat. No. 7,202,608 to Robinson
et al, U.S. Pat. No, 6,995,518, U.S. Pat. No. 6,724,376, U.S. Pat. No.
7,180,487 to Kamikawa et al, U.S. Pat. No. 6,614,358 to Hutchison et al,
U.S. Pat. No. 6,362,578 to Swanson et al, U.S. Pat. No. 5,661,645 to
Hochstein, U.S. Pat. No. 6,528,954 to Lys et al, U.S. Pat. No. 6,340,868
to Lys et al, U.S. Pat. No. 7,038,399 to Lys et al, U.S. Pat. No.
6,577,072 to Saito et al, and U.S. Pat. No. 6,388,393 to Illingworth.

[0010]In the general illumination application of solid state light
sources, one desirable characteristic is to be compatible with existing
dimming techniques. In particular, dimming that is based on varying the
duty cycle of the line voltage may present several challenges in power
supply design for solid state lighting. Unlike incandescent lamps, LEDs
typically have very rapid response times to changes in current. This
rapid response of LEDs may, in combination with conventional dimming
circuits, present difficulties in driving LEDs.

[0011]For example, one way to reduce the light output in response to the
phase cut AC signal is to utilize the pulse width of the incoming phase
cut AC line signal to directly control the dimming of the LEDs. The 120
Hz signal of the full-wave rectified AC line signal would have a pulse
width the same as the input AC signal. This technique limits the ability
to dim the LEDs to levels below where there is insufficient input power
to energize the power supply. Also, at narrow pulse width of the AC
signal, the output of the LEDs can appear to flicker, even at the 120 Hz
frequency. This problem may be exacerbated in 50 Hz systems as the full
wave rectified frequency of the AC line is only 100 Hz.

[0012]Furthermore, variation in the input signal may affect the ability to
detect the presence of a phase cut dimmer or may make detection
unreliable. For example, in systems that detect the presence of a phase
cut dimmer based on detection of the leading edge of the phase cut AC
input, if a reverse-phase cut dimmer is used, the dimming is never
detected. Likewise, many residential dimmers have substantial variation
in pulse width even without changing the setting of a dimmer. If a power
supply detects the presence of dimming based on a threshold pulse width,
the power supply could detect the presence of dimming on one cycle and
not on another as a result of this the variation in pulse width.

[0013]A further issue relates to AC dimmers providing some phase cut even
at "full on." If the LEDs are directly controlled by the AC pulse width,
then the LEDs may never reach full output but will dim the output based
on the pulse width of the "full on" signal. This can result in a large
dimming of output. For example, an incandescent lamp might see a 5%
reduction in power when the pulse width is decreased 20%. Many
incandescent dimmers have a 20% cut in pulse width at full on, even
though the RMS voltage is only reduced 5%. While this would result in a
5% decrease in output of an incandescent, it results in a 20% decrease in
output if the phase cut signal is used to directly control the LEDs.

SUMMARY OF THE INVENTION(S)

[0014]The dimming signal generation circuits described herein may provide
for a common basic circuit that may be used for differing types of
dimming signals, including dimming directly from a phase cut input AC
line, DC voltage level dimming (e.g., 0-10V DC dimming) and/or PWM
dimming. Embodiments of the present inventive subject matter may be
particularly well suited to controlling a drive circuit for solid state
lighting devices, such as LEDs.

[0015]Some embodiments of the present inventive subject matter provide a
lighting control circuit that comprises a dimming level detection circuit
configurable to generate a first voltage level signal corresponding to a
selected one of at least two different types of dimming signals. The
types of dimming signals comprise at least two of an alternating current
(AC) phase cut dimming signal, a direct current (DC) voltage level
dimming signal or a pulse-width modulated (PWM) dimming signal. The
circuit also includes a waveform generator configured to output a
periodic waveform and a comparator circuit configured to compare the
periodic waveform with the first voltage level signal to generate an
output waveform having a duty cycle corresponding to a dimming level of
the one of the at least two different input dimming signals and a
frequency corresponding to the frequency of the periodic waveform.

[0016]In some embodiments, the dimming level detection circuit is user
configurable to generate the voltage level from one of the at least two
different input dimming signals. In other embodiments, the dimming level
detection circuit is preconfigured to generate the voltage level from one
of the at least two different input dimming signals. In still further
embodiments, the dimming level detection circuit is configurable by
electrical jumper configuration. Additionally, the dimming level
detection circuit may be configurable by component selection and/or by
connection to different input connectors associated with the at least two
different types of dimming signals.

[0017]In further embodiments, the lighting control circuit further
comprises a shutdown comparator circuit which is configured to compare
the first voltage level signal with a shutdown threshold voltage and to
generate a shutdown signal based on the comparison.

[0018]The dimming level detection circuit may comprise a wired OR circuit
of voltage levels corresponding to the at least two different types of
dimming signals. The dimming level detection circuit may also comprise a
duty cycle detection circuit and an averaging circuit. The averaging
circuit may comprise a first averaging circuit configured to average a
detected duty cycle of an AC dimming signal and a second averaging
circuit configured to average a duty cycle of a PWM dimming signal.

DESCRIPTION OF THE DRAWINGS

[0019]FIGS. 1A through 1C are examples of a cycle of a full wave rectified
AC line signal with and without phase cut dimming.

[0020]FIG. 2 is a block diagram of a lighting device incorporating dimming
signal generation according to some embodiments of the present inventive
subject matter.

[0021]FIG. 3 is a block diagram of a lighting device suitable for use in
an AC phase cut, 0-10V and/or PWM dimming system according to some
embodiments of the present inventive subject matter.

[0022]FIG. 4 is a block diagram of a dimming signal generation circuit
according to some embodiments of the present inventive subject matter.

[0023]FIGS. 5A and 5B are waveform diagrams illustrating alternative duty
cycle detection techniques suitable for use in duty cycle detection
circuits according to some embodiments of the present inventive subject
matter.

[0024]FIGS. 6A and 6B are timing diagrams illustrating operation of
averaging, waveform generator and comparator circuits according to some
embodiments of the present inventive subject matter.

[0025]FIG. 7 is a block diagram of a dimming signal generation circuit
according to further embodiments of the present inventive subject matter.

[0026]FIG. 8 is a block diagram of a dimming signal generation circuit
according to further embodiments of the present inventive subject matter.

[0027]FIG. 9 is a circuit diagram of a dimming signal generation circuit
according to some embodiments of the present inventive subject matter.

[0028]FIG. 10 is a circuit diagram of a dimming signal generation circuit
utilizing asymmetric pulse width detection according to further
embodiments of the present inventive subject matter.

[0029]FIG. 11 is a circuit diagram of a dimming signal generation circuit
according to further embodiments of the present inventive subject matter.

[0030]FIG. 12 is a circuit diagram of a system as illustrated in FIG. 2
according to some embodiments of the present inventive subject matter.

[0031]FIG. 13 is a flowchart illustration of operations of some
embodiments of the present inventive subject matter.

[0032]FIG. 14 is a flowchart illustration of operations according to
further embodiments of the present inventive subject matter.

[0033]FIGS. 15A through 15E are representative examples of waveform shapes
for the waveform generator according to the present inventive subject
matter.

DETAILED DESCRIPTION OF THE INVENTION(S)

[0034]The present inventive subject matter now will be described more
fully hereinafter with reference to the accompanying drawings, in which
embodiments of the inventive subject matter are shown. However, this
inventive subject matter should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are provided so
that this disclosure will be thorough and complete, and will fully convey
the scope of the inventive subject matter to those skilled in the art.
Like numbers refer to like elements throughout. As used herein, the term
"and/or" includes any and all combinations of one or more of the
associated listed items.

[0035]The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of the
inventive subject matter. As used herein, the singular forms "a", "an"
and "the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood that
the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the presence
or addition of one or more other features, integers, steps, operations,
elements, components, and/or groups thereof.

[0036]As noted above, the various aspects of the present inventive subject
matter include various combinations of electronic components
(transformers, switches, diodes, capacitors, transistors, etc.). Persons
skilled in the art are familiar with and have access to a wide variety of
such components, and any of such components can be used in making the
devices according to the present inventive subject matter. In addition,
persons skilled in the art are able to select suitable components from
among the various choices based on requirements of the loads and the
selection of other components in the circuitry. Any of the circuits
described herein (and/or any portions of such circuits) can be provided
in the form of (1) one or more discrete components, (2) one or more
integrated circuits, or (3) combinations of one or more discrete
components and one or more integrated circuits.

[0037]A statement herein that two components in a device are "electrically
connected," means that there are no components electrically between the
components, the insertion of which materially affect the function or
functions provided by the device. For example, two components can be
referred to as being electrically connected, even though they may have a
small resistor between them which does not materially affect the function
or functions provided by the device (indeed, a wire connecting two
components can be thought of as a small resistor); likewise, two
components can be referred to as being electrically connected, even
though they may have an additional electrical component between them
which allows the device to perform an additional function, while not
materially affecting the function or functions provided by a device which
is identical except for not including the additional component;
similarly, two components which are directly connected to each other, or
which are directly connected to opposite ends of a wire or a trace on a
circuit board or another medium, are electrically connected.

[0038]Although the terms "first", "second", etc. may be used herein to
describe various elements, components, regions, layers, sections and/or
parameters, these elements, components, regions, layers, sections and/or
parameters should not be limited by these terms. These terms are only
used to distinguish one element, component, region, layer or section from
another region, layer or section. Thus, a first element, component,
region, layer or section discussed below could be termed a second
element, component, region, layer or section without departing from the
teachings of the present inventive subject matter.

[0039]Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this inventive
subject matter belongs. It will be further understood that terms, such as
those defined in commonly used dictionaries, should be interpreted as
having a meaning that is consistent with their meaning in the context of
the relevant art and the present disclosure and will not be interpreted
in an idealized or overly formal sense unless expressly so defined
herein.

[0040]FIG. 2 is a block diagram of a lighting device 10 incorporating
embodiments of the present inventive subject matter. As seen in FIG. 2,
the lighting device 10 includes a driver circuit 20 and one or more LEDs
22. The LED driver circuit 20 is responsive to a dimming signal generator
circuit 24. The dimming signal generator circuit 24 receives various
dimming signals, including two or more types of signals selected from (1)
an AC phase cut signal, (2) a pulse width modulated (PWM) dimming signal
and (3) a voltage level dimming signal (e.g., a 0-10V DC dimming
signal--in the description below, including descriptions of specific
embodiments, reference is made to 0-10V DC dimming signals as a
representative type of voltage level dimming signal--it should be
recognized, however, that any desired reference range of voltage, i.e.,
other than 0-10V, may be employed, and that higher relative voltage
levels can be indicative of a greater extent of dimming or can be
indicative of a lesser extent of dimming). In some embodiments, a
variable duty cycle input signal of a first frequency is provided to the
dimming signal generator circuit 24 and the circuit 24 outputs a fixed
amplitude signal having a second frequency different from the first
frequency and with a duty cycle that is dependent on the corresponding
input signal.

[0041]In operation, the dimming signal generator circuit 24 receives an
input dimming signal and outputs a waveform of a specified frequency
where the duty cycle of the output waveform is proportional to the level
of dimming. With regard to the variable duty cycle input signals (e.g.,
the AC phase cut signal or the PWM dimming signal), the generation of the
dimming signal involves generating an output signal having a duty cycle
that is proportional to the duty cycle of the input signal. With regard
to the 0-10V dimming, generation of the dimming signal involves
generating an output signal having a duty cycle that is proportional to
the voltage level of the 0-10V dimming signal.

[0042]With regard to input signals that have variable duty cycle (e.g.,
the AC phase cut signal or the PWM dimming signal), the duty cycle of the
output waveform of the dimming signal generator circuit 24 may be
substantially the same as the duty cycle of the input signal(s) or it may
differ according to a predefined relationship. For example, the duty
cycle of the output waveform may have a linear or non-linear relationship
to the duty cycle of the input signal. Likewise, the duty cycle of the
output waveform will typically not track the duty cycle of the input
waveform on a cycle by cycle basis. Such may be beneficial if substantial
variations may occur in the duty cycle of the variable duty cycle
waveform, for example as may occur in the output of a conventional AC
phase cut dimmer even without changing the setting of the dimmer.
Therefore, the output waveform of the dimming signal generator circuit 24
will, in some embodiments, have a duty cycle that is related to a
smoothed or average duty cycle of the input signal. This smoothing or
averaging of the input duty cycle may reduce the likelihood that
unintended variations in the duty cycle of the input waveform will result
in undesirable changes in intensity of the light output by the lighting
device 10 while still allowing for changes in the dimming level. Further
details on the operation of duty cycle detection and frequency conversion
circuits according to some embodiments of the present inventive subject
matter are provided below.

[0043]With regard to the 0-10V dimming signal, the duty cycle of the
output waveform of the dimming signal generator circuit 24 may vary
linearly, non-linearly or both with respect to the voltage level of the
input signal. For example, the duty cycle of the output waveform may have
a linear relationship to the voltage level of the input signal over a
first range of voltages and a fixed or non-linear relationship over
another range of voltages. In particular, the duty cycle of the output
waveform may be reduced to a minimum duty cycle when the input voltage
level is reduced from 10V to 1V and then maintained at that minimum duty
cycle from 1V to 0V. Likewise, the duty cycle of the output waveform will
typically not track minor variations in dimming signal voltage level.
Such may be beneficial if variations may occur in the voltage level of
the dimming signal without changing the setting of the dimmer. Therefore,
the output waveform of the dimming signal generator circuit 24 will, in
some embodiments, have a duty cycle that is related to a smoothed or
average of the voltage level of the input signal. This smoothing or
averaging of the voltage level may reduce the likelihood that unintended
variations in the voltage level of the input waveform will result in
undesirable changes in intensity of the light output by the lighting
device 10 while still allowing for changes in the dimming level.

[0044]The driver circuit 20 may be any suitable driver circuit capable of
responding to a pulse width modulated input that reflects the level of
dimming of the LEDs 22. The particular configuration of the LED driver
circuit 20 will depend on the application of the lighting device 10. For
example, the driver circuit may be a boost or buck power supply.
Likewise, the LED driver circuit 20 may be a constant current or constant
voltage pulse width modulated power supply. For example, the LED driver
circuit may be as described in U.S. Pat. No. 7,071,762. Alternatively,
the LED driver circuit 20 may be a driver circuit using linear
regulation, such as described in U.S. Pat. No. 7,038,399 and in U.S.
Patent Application No. 60/844,325, filed on Sep. 13, 2006, entitled
"BOOST/FLYBACK POWER SUPPLY TOPOLOGY WITH LOW SIDE MOSFET CURRENT
CONTROL" (inventor: Peter Jay Myers; attorney docket number 931--020
PRO), and U.S. patent application Ser. No. 11/854,744, filed Sep. 13,
2007 entitled "Circuitry for Supplying Electrical Power to Loads," the
disclosures of which are incorporated herein by reference as if set forth
in their entirety. The particular configuration of the LED driver circuit
20 will depend on the application of the lighting device 10.

[0045]FIG. 3 illustrates further embodiments of the present inventive
subject matter where a lighting device 30 is powered from an AC line
input where the duty cycle of the AC line input varies. Such an input
may, for example, be provided by utilizing a phase cut dimmer to control
the duty cycle of the AC line input. The lighting device 30 includes one
or more LEDs 22, an LED driver circuit 40, a power supply 42 and a
dimming signal generator circuit 44. The power supply 42 receives an AC
line input and provides power to the LED driver circuit 40 and the
dimming signal generator circuit 44. The power supply 42 may be any
suitable power supply including, for example, buck or boost power
supplies as described in U.S. patent application Ser. No. 11/854,744.
Also, the LED driver circuit 40 may be any suitable LED driver circuit
capable of varying the intensity of the output of the LEDs 22 in response
to a fixed amplitude signal of variable duty cycle. The particular
configurations of the LED driver circuit 40 and/or the power supply 42
will depend on the application of the lighting device 30.

[0046]The dimming signal generator circuit 44 is configured to receive at
least two of (1) a PWM dimming signal, (2) a 0-10V dimming signal and (3)
a rectified AC input that reflects a phase cut AC dimming signal. The
dimming signal generator circuit 44 receives whichever signal (or
signals) is being utilized for the dimming signal (always or at a
particular time) and converts that signal into a pulse width modulated
signal of a known frequency.

[0047]As is further seen in FIG. 3, the dimming signal generator circuit
44 is configured to receive the rectified AC input from the power supply
42 and detects the duty cycle of the rectified AC input. By detecting
duty cycle rather than RMS voltage, the diming signal generator circuit
44 may be less sensitive to variations in the AC input voltage (for
example, if duty cycle were estimated by instead tracking RMS voltage, an
AC line voltage drop from 120 VAC to 108 VAC would bring about an
incorrect reduction in the estimated duty cycle, i.e., variations in
input voltage may be misinterpreted as changes in duty cycle and result
in an undesired dimming of the light output). In contrast, by detecting
duty cycle rather than RMS voltage, variations in the voltage level will
only be reflected as small variations in the detected duty cycle that
result from changes in slew rate for the voltage to reach the differing
voltage levels.

[0048]In addition to generating a known frequency, fixed amplitude
waveform having a duty cycle that is related to the dimming information
of the input wave form, the dimming signal generator circuits 24 and/or
44 of FIGS. 2 and/or 3 may also detect when the dimming signal of the
input waveform has fallen below a maximum dimming level and output a
shutdown signal. The shutdown signal may be provided to the power supply
42 and/or the LED driver circuit 20 or 40. In some embodiments, the
shutdown signal may be provided to turn off the LEDs at a time before the
input power to the lighting device 10 or 30 reaches a level that is below
a minimum operating level of the lighting device 10 or 30. Alternatively
or additionally, the shutdown signal may be provided to turn off the LEDs
at a time before the power drawn by the lighting device 10 or 30 reaches
a level that is below a minimum operating power for a dimmer control
device, such as a triac dimmer or other phase cut dimmer.

[0049]FIG. 4 illustrates functional blocks for a dimming signal generator
circuit 100 according to some embodiments of the present inventive
subject matter. The dimming signal generator circuit 100 is configured to
receive variable duty cycle AC waveform inputs (phase cut AC dimmings
signals), PWM dimming signal inputs, and/or 0-10V dimming signal inputs.
For variable duty cycle AC waveform inputs, the dimming signal generator
circuit 100 utilizes pulse width detection of a variable duty cycle
waveform to provide a duty cycle detection circuit 110. The output of the
duty cycle detection circuit 110 is a fixed amplitude waveform with a
duty cycle corresponding to (i.e., based on, but not necessarily
differing from) the duty cycle of the input waveform (e.g., depending on
the embodiment according to the present inventive subject matter, similar
to, slightly less than, related to or inversely related to the duty cycle
of the input waveform). The expression "related to" encompasses
relationships where the variance of the duty cycle of the output of the
duty cycle detection circuit is proportional to the variance of the duty
cycle of the input waveform (i.e., there is a linear relationship between
the two), or where there is no linear relationship and if the duty cycle
of the input waveform increases, the duty cycle of the output of the duty
cycle detection circuit also increases, and vice-versa (i.e., if the duty
cycle of the input waveform decreases, the duty cycle of the output of
the duty cycle detection circuit also decreases); conversely, the
expression "inversely related to" encompasses relationships where the
variance of the duty cycle of the output of the duty cycle detection
circuit is inversely proportional to the variance of the duty cycle of
the input waveform, or where there is no linear inverse relationship and
if the duty cycle of the input waveform decreases, the duty cycle of the
output of the duty cycle detection circuit increases, and vice-versa.

[0050]The output of the duty cycle detection circuit 110 is provided to an
averaging circuit 120 that creates an average value of the output of the
duty cycle detection circuit. Likewise, because the PWM dimming signal is
a fixed amplitude square wave with a variable duty cycle, if PWM dimming
is utilized, the PWM dimming signal may be provided directly to an
averaging circuit 120. In some embodiments, the average value of the
respective square waves is reflected as a voltage level.

[0051]A high frequency waveform is provided by the waveform generator 130.
The waveform generator 130 may generate a triangle, sawtooth or other
periodic waveform. In some embodiments, the frequency of the waveform
output by the waveform generator 130 is greater than 200 Hz, and in
particular embodiments, the frequency is about 300 Hz (or higher). The
shape of the waveform may be selected to provide the desired relationship
between the dimming information contained in the input signal (duty cycle
or voltage level) and the duty cycle of the pulse width modulated (PWM)
output signal. The output of the waveform generator 130 and the output of
the averaging circuit 120 or the input voltage level of the 0-10V dimming
signal are compared by the comparator 140 to generate a periodic waveform
with the frequency of the output of the waveform generator 130 and a duty
cycle based on the voltage level of output of the averaging circuit 120
or the 0-10V dimming signal.

[0052]Operation of a first embodiment of a dimming signal generator
circuit 100 will now be described with reference to the waveform diagrams
of FIGS. 5A, 5B, 6A and 6B. In particular, FIGS. 5A and 5B illustrate
duty cycle detection utilizing a symmetric threshold (FIG. 5A) and
alternative embodiments utilizing asymmetric thresholds (FIG. 5B). In
either case, the voltage level of the input waveform is compared to a
threshold voltage.

[0053]In the symmetric example (FIG. 5A), if the input voltage (phase cut
AC dimming signal) is above the threshold voltage, the output of the duty
cycle detection circuit 110 is set to a first voltage level (in this
embodiment, 10 volts) and if the input voltage level is below the
threshold voltage, the output of the duty cycle detection circuit 110 is
set to a second voltage level (in this embodiment, 0 volts, i.e.,
ground). Thus, the output of the duty cycle detection circuit 110 is a
square wave that transitions between the first voltage level and the
second voltage level (e.g., 10 V and ground). The first and second
voltage levels may be any suitable voltage levels and may be selected
based upon the particular averaging circuit utilized.

[0054]In the asymmetric example (FIG. 5B), if the input voltage is above a
first threshold, the output of the duty cycle detection circuit 110 is
set to a first voltage level and remains at that voltage level until the
input voltage level falls below a second threshold voltage at which time
the output of the duty cycle detection circuit 110 is set to a second
voltage level. Thus, in the asymmetric example, the output of the duty
cycle detection circuit 110 is also a square wave that transitions
between the first voltage level and the second voltage level (e.g., 10 V
and ground). As described above, the first and second voltage levels may
be any suitable voltage levels and may be selected based upon the
particular averaging circuit utilized. The asymmetric detection may allow
for compensation for variations in the input waveform. For example, if
the leading or trailing edges of a phase cut waveform intermittently
include a section with a shallow slope followed or preceded by a section
with a steep slope, the separate thresholds could be set to align with
the section of steep slope so as to avoid minor variations in duty cycle
being amplified by the shallow slope portions of the waveform.

[0055]FIG. 6A illustrates operation of the averaging circuit 120. As seen
in FIG. 6A, the averaging circuit 120 averages a fixed amplitude periodic
waveform (output by the duty cycle detection circuit or the PWM dimming
signal input) with varying duty cycle to provide an averaged square wave
signal having a voltage that (in this embodiment) represents the duty
cycle of the phase cut AC dimming signal or the PWM dimming signal. The
level of averaging may be set to smooth out variations in the duty cycle
of the dimming signal. The input to the averaging circuit 120 may be a
PWM dimming signal or the output of the duty cycle detection circuit 110.

[0056]Accordingly, where a phase cut AC dimming signal is supplied, this
embodiment thus provides an averaged square wave signal which is related
to the duty cycle of the input voltage. For example, if (1) the duty
cycle of the phase cut AC dimming signal is 60%, (2) the duty cycle of
the output of the duty cycle detection circuit is 55%, (3) the first
voltage level is 10 V and (4) the second voltage level is 0 V, the
voltage of the averaged square wave signal would be about 5.5 V.
Alternatively, in other embodiments according to the present inventive
subject matter, the averaged square wave signal can instead be inversely
related to the duty cycle of the phase cut AC dimming signal. For
example, if the first voltage level is ground and the second voltage
level is 10 V, the inverse relationship would be provided (to illustrate,
for such an embodiment, if (1) the duty cycle of the phase cut AC dimming
signal is 85% and the threshold voltage is 0 V (e.g., zero cross
detection AC sensing is employed), the duty cycle of the output of the
duty cycle detection circuit would be 15% (i.e., for 85% of the time, the
voltage level would be ground, which is the first voltage level, and for
15% of the time, the voltage level would be 10 V, which is the second
voltage level), such that the voltage of the averaged square wave signal
would be about 1.5 V (whereas if the duty cycle of the input voltage were
10%, the voltage of the averaged square wave signal would be about 9 V).

[0057]It should also be noted that it is not necessary for either of the
first voltage level or the second voltage level to be zero. For instance,
if (1) the duty cycle of the phase cut AC dimming signal is 80%, (2) the
duty cycle of the output of the duty cycle detection circuit is 70%, (3)
the first voltage level is 20 V and (4) the second voltage level is 10 V,
the voltage of the averaged square wave signal would be about 17 V (i.e.,
the voltage of the averaged square wave signal would be between 10 V and
20 V, and would vary within that range proportionally to the duty cycle
of the output of the duty cycle detection circuit).

[0058]FIG. 6B illustrates the generation of the frequency shifted variable
duty cycle output. As seen in FIG. 6B, while the input voltage to the
comparator (i.e., the output of the averaging circuit 120 or the 0-10V
dimming signal) is greater than the voltage of the output of the waveform
generator 130, the output of the comparator 140 is set to a first voltage
level, and while the value of the output of the averaging circuit 120 (or
the 0-10V dimming signal) is below the voltage of the output of the
waveform generator 130, the output of the comparator 140 is set to a
second voltage level, e.g., ground (i.e., whenever the plot of the
voltage of the averaging circuit (or the 0-10V dimming signal) crosses
the plot of the output of the waveform generator to become larger than
the output of the waveform generator, the output of the comparator is
switched to the first voltage level, and whenever the plot of the voltage
of the averaging circuit (or the 0-10V dimming signal) crosses the plot
of the output of the waveform generator to become smaller than the output
of the waveform generator, the output of the comparator is switched to
the second voltage level). Thus, the output of the comparator 140 is a
square wave that transitions between the first voltage level and the
second voltage level (e.g., 10 V and ground), has a duty cycle that
corresponds to the level of the voltage (1) output by the averaging
circuit 120 or (2) input as a 0-10V dimming signal, and has a frequency
corresponding to the frequency of the output of the waveform generator
130. The first and second voltage levels may be any suitable voltage
levels and may be selected based upon the particular LED driver circuit
with which the duty cycle detection and frequency conversion circuit 100
is being utilized.

[0059]In embodiments in which the duty cycle of the duty cycle detection
circuit is inversely related to the input voltage (as discussed above),
while the voltage of the averaged square wave signal (i.e., the output of
the averaging circuit 120) (or the 0-10V dimming signal) is greater than
the voltage of the output of the waveform generator 130, the output of
the comparator 140 is instead set to a second voltage level (e.g.,
ground), and while the value of the output of the averaging circuit 120
(or the 0-10V dimming signal) is below the voltage of the output of the
waveform generator 130, the output of the comparator 140 is instead set
to a first voltage level, with the result that, as with the embodiment
shown in FIG. 6B, the comparator 140 is a square wave that transitions
between the first voltage level and the second voltage level (e.g., 10 V
and ground), has a duty cycle that corresponds to the level of the
voltage output by the averaging circuit 120 (or that inversely
corresponds to the voltage level of the 0-10V dimming signal) and has a
frequency corresponding to the frequency of the output of the waveform
generator 130.

[0060]While FIG. 6B illustrates a generated waveform in the shape of a
triangular sawtooth, any desired waveform shape can be employed. For
example, the waveform can be of any of the shapes depicted in FIGS. 15A
through 15E. FIG. 15A shows a non-linear waveform which includes linear
portions 201 and curved portions 202 in a repetitive pattern. FIG. 15B
shows a non-linear waveform which also includes linear portions 201 and
curved portions 202 in a repetitive pattern. FIG. 15C shows a linear
waveform which includes linear portions 201 and 203 which are of
differing steepness (i.e., absolute value of slope). FIG. 15D shows a
linear waveform which consists of a repeating pattern which includes two
differently-shaped sub-portions 204 and 205. FIG. 15E shows a non-linear
waveform which consists of a repeating pattern which includes two
differently-shaped sub-portions 206 and 207. It is readily seen that
there are an infinite number of possible waveforms, and persons skilled
in the art can readily select any desired waveform in order to achieve
desired characteristics.

[0061]As can be seen from FIGS. 5A through 6B, the shape of the waveform
output from the waveform generator 130 may affect the relationship
between (1) the input dimming signal (i.e., the phase cut AC dimming
signal, the 0-10V dimming signal and/or the PWM dimming signal) and (2)
the output duty cycle of the dimming signal generator circuit 100. If the
waveform is linear (i.e., consists of linear and/or substantially linear
segments) in the range over which the voltage output by the averaging
circuit 120 and the 0-10V dimming signal operate, then the relationship
between input dimming signal and output duty cycle will be linear. If the
waveform is non-linear in at least part of the range over which the
voltage output by the averaging circuit 120 or the 0-10V dimming signal
operates, then the relationship between input dimming signal and output
duty cycle will be non-linear.

[0062]Likewise, offsets between the input dimming signal and the output
duty cycle may be provided by a DC offset which adjusts the waveform
output from the waveform generator 130 and/or the voltage level output
from the averaging circuit 120. For example, in a system in which the
voltage level of the averaged square wave is related to (or proportional
to) the duty cycle of the phase cut AC dimming signal or the PWM dimming
signal, and in which the frequency shifted variable duty cycle output is
a first voltage level when the voltage of the averaged square wave signal
or the 0-10V dimming signal is greater than the voltage of the output of
the waveform generator, if the output of the waveform generator 130 is
offset such that the highest voltage level reached by the waveform is
lower than the voltage output by the averaging circuit 120 with duty
cycles of 90% or higher, then the output of the comparator would be a
constant (DC) signal at the first voltage level except when the duty
cycle of the input waveform falls below (i.e., is less than) 90% (and
likewise when the 0-10V dimming signal is 9V or higher). Alternatively, a
minimum threshold could also be set, for example, to comply with maximum
dimming at the 1V level requirements of particular 0-10V dimming systems.
Such variations could be made adjustable and/or selectable, for example,
by a user. A variety of other relationships could be used, e.g., if the
voltage level of the averaged square wave is inversely related to the
duty cycle of the input voltage, and the frequency shifted variable duty
cycle output is a first voltage level when the voltage of the averaged
square wave signal is less than the voltage of the output of the waveform
generator, the waveform generator can be offset such that the lowest
voltage level reached by the waveform is higher than the voltage output
by the averaging circuit with duty cycles of 90% or higher, such that the
output of the comparator would likewise be a constant (DC) signal at the
first voltage level except when the duty cycle of the input waveform
falls below 90%.

[0063]Another representative example of an offset that can optionally be
provided is a DC offset in which the voltage output by the averaging
circuit is increased by a specific amount (i.e., in systems where the
voltage level of the averaged square wave is related to the duty cycle of
the input voltage) or decreased by a specific amount (i.e., in systems
where the voltage level of the averaged square wave is inversely related
to the duty cycle of the input voltage). Such an offset can be useful for
a variety of purposes, e.g., to compensate for a circuit in which duty
cycle detection (symmetric or asymmetric) does not use zero cross
detection, such that even a 100% duty cycle rectified power signal would
not produce a constant signal (i.e., where the voltage depicted in FIG.
6A would be at the first voltage level 100% of the time). In such a
situation, the voltage output by the averaging circuit could be increased
such that where the duty cycle of the rectified power signal is 100%, the
output of the averaging circuit is representative of a 100% duty cycle
power signal (even though the output of the duty cycle detection circuit
generated in response to the input waveform exhibits the first voltage
level only part of the time, e.g., 95% of the time (and thus the averaged
square wave represents a percentage duty cycle which is higher, e.g., by
5%, than the percentage of the time that the square wave representation
of AC phase cut exhibits the first voltage level).

[0064]FIG. 7 illustrates further embodiments of the present inventive
subject matter where the dimming signal generator circuit 200 also
includes a minimum pulse width detection feature. Many triac based
dimmers have performance problems at light load levels which can be
present with LED based lighting products at low duty cycle dimming
levels. If the triac dimmers fall below their minimum load level, their
output may be unpredictable, which may result in unpredictable output
from a lighting device connected to the dimmer. Likewise, if the pulse
width is too small, the minimum voltage requirements of the lighting
device may not be met and the power supply might be starved for power.
This condition may also be undesirable. As such, the ability to shut down
a power supply or lighting device before the undesirable conditions
resulting from low pulse width on the line input can avoid unpredictable
and undesirable performance of the lighting device. Thus, the minimum
pulse width detection circuit 150 allows for setting the low level
dimming point by detecting when the voltage output by the averaging
circuit 120 (or the 0-10V dimming signal) falls below (or above, in
embodiments where the duty cycle of the output of the duty cycle
detection circuit is inversely related to the duty cycle of the input
voltage) a threshold voltage associated with the minimum duty cycle for
which the lighting device and/or dimmer will operate reliably.

[0065]FIG. 8 illustrates still further embodiments of the present
inventive subject matter. As seen in FIG. 8, the dimming signal generator
circuit 300 includes a slope adjust circuit 160. The slope adjust circuit
160 provides a method to offset the duty cycle ratio between the duty
cycle determined from the variable duty cycle waveform, such as a
rectified AC line with phase cut dimming (or voltage level of the 0-10V
dimming signal), and the PWM output provided to the LED driver circuit.
This would allow for a lower light level while still maintaining a
sufficient AC voltage from the triac dimmer to power a lighting device.

[0066]FIG. 9 is a circuit diagram of a dimming signal generator circuit
100 according to some embodiments of the present inventive subject
matter. As seen in FIG. 9, the rectified AC line voltage is scaled to
appropriate voltage levels, for example, by dividing the voltage down
through a resistor divider network, and sent to the positive input of a
first comparator U1. The comparator U1 compares the scaled and rectified
AC to a fixed voltage reference (Vthr) at the negative input. When
the positive input exceeds the negative, the output of the comparator U1
is high; when the reverse is true, the output is low (on the other hand,
in embodiments where the duty cycle of the output of the duty cycle
detection circuit is inversely related to the duty cycle of the input
voltage, the comparator U1 is reversed, such that the rectified AC input
voltage is supplied to the negative input of the comparator U1 and the
fixed voltage reference is supplied to the positive input of the
comparator U1). The resultant waveform is a close representation of the
non-zero voltage duty-cycle of the AC line (the closer the fixed voltage
reference Vthr is to zero, the closer the resultant waveform
approximates the non-zero voltage duty cycle of the AC line). The
resultant waveform is a fixed amplitude square wave with a duty cycle and
a frequency which correspond to the duty cycle and frequency of the
rectified AC line. The reference voltage Vthr sets the maximum pulse
width of the square wave output of the comparator U1. The closer the
reference voltage Vthr is to zero volts, the greater the maximum
pulse width (for example, if Vthr is 5 V, the maximum pulse width is
100% minus the percentage of the time that the pulse is less than 5 V
(the percentage of the time that the pulse is less than 5 V corresponding
to the percentage of the plot, viewed along the x axis, where the plot is
less than 5 V)). In some embodiments, the reference voltage may be set to
a value that reduces or eliminates half cycle imbalances in a rectified
triac phase cut AC waveform. Skilled artisans are familiar with ways to
make the reference voltage zero (or very close to zero), e.g., by
providing AC sensing detection, such as zero cross detection.

[0067]The variable duty-cycle fixed amplitude square wave from the duty
cycle detection circuit 110 is then filtered by the averaging circuit 120
to create an average value; higher level for higher duty-cycles, lower
level for lesser duty-cycles (the opposite is of course true in
embodiments where the duty cycle of the output of the duty cycle
detection circuit is inversely related to the duty cycle of the input
voltage). Because the square wave is of fixed amplitude, the average
value is proportional to the duty cycle of the square wave, which is
proportional to the duty-cycle of the input waveform, such as the AC line
input. The averaging circuit 120 is illustrated as a filter that includes
resistor R1 and capacitor C1. While a single stage RC filter is
illustrated in FIG. 9, other filtering or averaging techniques could be
utilized. For example, in some embodiments, an RC filter with two or more
stages may be used.

[0068]The averaging circuit 120 may also receive the PWM dimming signal,
which is buffered by U7 (which may also translate the voltage level of
the input signal to correspond to the voltage level of the output of the
comparator U1), and provided to a filter. The filter is illustrated as an
RC filter comprising R5 and C3. Alternative filter arrangements may also
be utilized. The particular filter characteristics may, for example,
depend on the frequency of the PWM dimming signal, the rate of change in
duty cycle of the PWM dimming signal and the voltage level of the input.
For example, the filter may be adjusted to filter out minor variations in
duty cycle on a cycle by cycle basis.

[0069]Additionally, in some embodiments, the 0-10V dimming signal may be
received by the buffer U6 and the voltage level adjusted so as to be
compatible with the comparator circuit 140. The voltage conversion may be
carried out by the buffer U6 and/or through resistor divider (not shown)
or other techniques known to those of skill in the art.

[0070]The output(s) of the averaging circuit 120 and, optionally, the
0-10V dimming signal is/are provided (through respective diodes D1, D2
and D3 that provide an "OR" of the voltage levels) to the positive input
of a second comparator U3 and is compared to a fixed-frequency
fixed-amplitude triangle/sawtooth wave generated by the op amp (i.e.,
operational amplifier) U2, resistors R2, R3 and R4 and the capacitor C2.
The triangle/sawtooth waveform is connected to the negative input of the
comparator U3 (in embodiments in which the duty cycle of the output of
the duty cycle detection circuit is inversely related to the duty cycle
of the input voltage, the waveform is instead connected to the positive
input of the comparator U3). The output of the comparator U3 is a square
wave which has a duty-cycle proportional to the voltage level at the
positive input of the comparator U3 (the output of the averaging circuit
120) and a frequency equal to that of the triangle/sawtooth wave. In this
manner, the duty cycle of, for example, a lower frequency AC line can be
translated to a higher frequency square wave. The square wave can be used
to gate LEDs on and off for a dimming effect.

[0071]FIG. 9 illustrates the use of a single op amp sawtooth generator as
the waveform generator 130. Other circuits may also be utilized to
generate appropriate waveforms. For example, a two op amp triangle
oscillator as described on page A-44 of "Op Amps for Everyone," R.
Mancini, Editor, September 2000, may also be utilized. Other circuits
known to those of skill in the art may also be used. When using a
waveform generator such as illustrated in FIG. 9, to provide a linear
relationship (or substantially linear relationship) between input and
output duty cycle, the portions of the resulting waveform for the range
over which the average value voltage will vary should be linear (or
substantially linear). For example, the waveform generator illustrated in
FIG. 9 may provide a waveform with a linear region and a non-linear
region that resembles a "shark fin." If the range of voltages output by
the averaging circuit 120 overlaps with the non-linear region, then a
small change in input duty cycle could result in a large change in output
duty cycle, or vice-versa. Such a situation may make the overall circuit
susceptible to noise or too sensitive to variations in input duty cycle
(e.g. too sensitive to user input at a dimmer). As a result, the circuit
illustrated in FIG. 9 may be implemented such that the voltage range of
the averaging circuit 120 corresponds to a linear portion or portions of
the output waveform from the waveform generator 130.

[0072]As will be appreciated by those of skill in the art in light of the
present disclosure, the "OR" function provided by the diodes D1, D2 and
D3 may be provided by providing a low voltage level as an input to the
corresponding diode for unused dimming signal inputs. For example, the
0-10V dimming input could be pulled low unless connected to a dimmer
which would reverse bias the diode D3 when a signal was applied from
either the PWM dimming signal input or from the scaled and rectified AC
input.

[0073]FIG. 10 is a circuit diagram of a dimming signal generator circuit
100' that provides asymmetric threshold voltages for duty cycle
detection. As seen in FIG. 10, the duty cycle detection circuit 110'
includes a second comparator U4, a logic AND gate A1 and a Set/Reset
latch L1 that provide independently settable on and off thresholds. As
discussed above, the triac based AC waveform can have half cycle
imbalances that the voltage threshold(s) critical may be set based upon
to provide steady PWM duty cycle generation. The dimming signal generator
circuit 100' could also incorporate the PWM dimming signal and 0-10V
dimming signal circuitry as illustrated in FIG. 9.

[0074]In operation, the duty cycle detection circuit 110' sets the latch
L1 when the input voltage becomes higher than the threshold voltage
V1 and resets the latch L1 when the input voltage falls below the
threshold voltage V2, where V1>V2. In particular, when
the input voltage exceeds V1, the output of the comparator U1 is
high and the set input S of the latch L1 is high so as to cause the
output Q of the latch L1 to go high. When the input voltage falls below
V1, the output of the comparator U1 goes low but the output Q of the
latch L1 remains high. When the input further falls below V2, the
output of the comparator U4 goes high, therefore both inputs to the AND
gate A1 are high so the output of the AND gate A1 goes high, resetting
the latch L1, and the output Q goes low. While the circuit illustrated in
FIG. 10 has been designed for V1>V2, a corresponding circuit
where V1<V2 could be readily provided by logically ANDing
the inverted output of the latch L1 with the output of comparator U1 and
using the output of the AND as the set signal for the latch L1. In such a
case, the AND gate A1 could be eliminated and the output of the
comparator U4 provided directly to the rest of the latch L1.

[0075]FIG. 11 is a circuit diagram illustrating a dimming signal generator
circuit 200 that incorporates a minimum pulse width detection circuit
150. As seen in FIG. 11, the minimum pulse width detection circuit 150 is
provided by the comparator U5. In particular, a reference voltage
Vshut is provided to one input of the comparator U5 and the "ORed"
output of the averaging circuit 120 and/or 0-10V dimming signal is
provided to the other input. In this embodiment, the output of the
averaging circuit is related to the output of the duty cycle detection
circuit or the PWM dimming signal. When the output of the averaging
circuit or the 0-10V dimming signal falls below the reference voltage
Vshut, the output of the comparator U5 goes high, thus providing a
shutdown signal. In alternative embodiments, in which the output of the
averaging circuit is inversely related to the output of the duty cycle
detection circuit or the PWM dimming signal, the output of the comparator
U5 goes high to provide a shutdown signal when the output of the
averaging circuit or an inverted version of the 0-10V dimming signal
rises above the reference voltage Vshut.

[0076]FIG. 12 is a circuit diagram of a dimming signal generator circuit
100 coupled to an LED driver circuit where the string of LEDs (LED1, LED2
and LED3) is driven by an input voltage that is modulated by a high
frequency drive signal through the transistor T1. The diode D4, capacitor
C3 and inductor L1 provide current smoothing between cycles of the high
frequency drive signal. The resistor R5 provides a current sense that can
be fed back to a driver controller that varies the duty cycle of the high
frequency drive signal to provide constant current to the LEDs. The gate
of the transistor T1 is controlled by the driver DR1. The driver is
enabled by the output of the dimming signal generator circuit 100 so that
the high frequency drive signal is controlled by the output of the
dimming signal generator circuit 100. Because the transistor Ti is
controlled by the output of the dimming signal generator circuit 100, it
may be necessary to disable or otherwise control or compensate for the
current sense feedback to the controller when the transistor T1 is off,
as the sensed current feedback is only valid when the transistor T1 is
on.

[0077]FIGS. 13 and 14 are flowchart illustrations of operations according
to some embodiments of the present inventive subject matter. It will be
appreciated that the operations illustrated in FIGS. 13 and 14 may be
carried out simultaneously or in different sequences without departing
from the teachings of the present inventive subject matter. Thus,
embodiments of the present inventive subject matter should not be
construed as limited to the particular sequence of operations illustrated
by the flowcharts. Furthermore, operations illustrated in the flowcharts
may be carried out entirely in hardware or in combinations of hardware
and software.

[0078]Turning to FIG. 13, the type of dimming is initially determined
(block 470). If the type of dimming is AC phase cut dimming (block 470),
the duty cycle of the input waveform is detected to provide a fixed
amplitude duty cycle signal (block 500). The average is determined of the
fixed amplitude signal to generate an average value which may be
reflected as a voltage level (block 510). A waveform of a different
frequency from the frequency of the input signal is generated (block 520)
and the value of the waveform is compared to the average value (voltage
level) to generate a waveform with a duty cycle corresponding to (i.e.,
not necessarily the same as, but "based on") the input duty cycle at a
frequency corresponding to the frequency of the generated waveform (block
530).

[0079]If the type of dimming is PWM dimming (block 470), the amplitude of
the input PWM signal is adjusted to provide a fixed amplitude variable
duty cycle signal (block 490). The average is determined of the fixed
amplitude signal to generate an average value which may be reflected as a
voltage level (block 510). A waveform of a different frequency from the
frequency of the input signal is generated (block 520) and the value of
the waveform is compared to the average value (voltage level) to generate
a waveform with a duty cycle corresponding to (i.e., not necessarily the
same as, but "based on") the input duty cycle at a frequency
corresponding to the frequency of the generated waveform (block 530).

[0080]If the type of dimming is 0-10V dimming (block 470), the amplitude
of the input dimming signal is adjusted to scale to the appropriate
voltage level (block 480). A waveform of a different frequency from the
frequency of the input signal is generated (block 520) and the value of
the waveform is compared to the generated voltage level to generate a
waveform with a duty cycle corresponding to (i.e., not necessarily
linearly related to, but "based on") the voltage level dimming signal at
a frequency corresponding to the frequency of the generated waveform
(block 530).

[0081]FIG. 14 illustrates further operations according to some embodiments
of the present inventive subject matter. As seen in FIG. 14, the type of
dimming is determined (block 570). If the dimming is AC phase cut dimming
(block 570), the duty cycle of the input waveform is detected to provide
a fixed amplitude signal with a duty cycle corresponding to the duty
cycle of the input waveform (block 600). The average value of the fixed
amplitude signal is determined to generate an averaged voltage
corresponding to the average value of the fixed amplitude signal (block
610). The averaged voltage level is compared to a voltage level for the
minimum pulse width to determine if the pulse width of the input signal
is less than the minimum allowable pulse width (block 620). If the
averaged voltage level is below this level (block 620), the shutdown
signal is provided (block 670). If the averaged voltage level is above
the minimum allowable pulse width level (block 620), the averaged voltage
level is compared to the voltage of a generated waveform (block 640). The
generated waveform may be of a frequency different from that of the input
signal (block 630). If the averaged voltage level is above the voltage of
the generated waveform (block 640), a high signal is output (block 650).
If the averaged voltage is below the voltage of the generated waveform
(block 640), a low signal is output (block 660).

[0082]If the dimming is PWM dimming (block 570), the amplitude of the
input signal is adjusted to provide a fixed amplitude signal (block 600).
The average value of the fixed amplitude signal is determined to generate
an averaged voltage corresponding to the average value of the fixed
amplitude signal (block 610). The averaged voltage level is compared to a
voltage level for the minimum pulse width to determine if the pulse width
of the input signal is less than the minimum allowable pulse width (block
620). If the averaged voltage level is below this level (block 620), the
shutdown signal is provided (block 670). If the averaged voltage level is
above the minimum allowable pulse width level (block 620), the averaged
voltage level is compared to the voltage of a generated waveform (block
640). The generated waveform may be of a frequency different from that of
the input signal (block 630). If the averaged voltage level is above the
voltage of the generated waveform (block 640), a high signal is output
(block 650). If the averaged voltage is below the voltage of the
generated waveform (block 640), a low signal is output (block 660).

[0083]If the dimming is 0-10V dimming (block 570), the amplitude of the
input signal is adjusted to provide a voltage level within a predefined
range corresponding to the range of average value voltage levels (block
580). The voltage level is compared to a voltage level for the minimum
pulse width to determine if the pulse width of the input signal is less
than the minimum allowable pulse width (block 620). If the voltage level
is below this level (block 620), the shutdown signal is provided (block
670). If the voltage level is above the minimum allowable pulse width
level (block 620), the voltage level is compared to the voltage of a
generated waveform (block 640). The generated waveform may be of a
frequency different from that of the input signal (block 630). If the
averaged voltage level is above the voltage of the generated waveform
(block 640), a high signal is output (block 650). If the averaged voltage
is below the voltage of the generated waveform (block 640), a low signal
is output (block 660).

[0084]The generation of a square wave representation of an input waveform
duty cycle, such as the AC line voltage, in this manner is tolerant of
variations in line voltage and frequency, i.e. the square wave will
remain the same even if the AC line voltage or frequency increases or
decreases due to utility generation, load adding or shedding, or other
reasons. A circuit which, unlike the present invention, filters the
rectified line would be unable to differentiate between changes in duty
cycle and changes in line voltage, and the representative filtered level
would change in response--the present inventive subject matter overcomes
these drawbacks.

[0085]The generated waveform used as the comparison source for the final
output may be altered in frequency or shape. Altering the shape of the
generated waveform can change the proportional response of the output to
the input dimming signal, e.g., if desired, to create a highly non-linear
dimming response to the input dimming signal.

[0086]The higher frequency output, used as a manner to switch on and off
the LEDs, can eliminate human visible flicker, and/or the flicker as
recorded by electronics such as video cameras.

[0087]Using the methods and circuits according to the present inventive
subject matter, a light or a set of lights connected to a driver as
described herein can be connected to a power source, through a circuit in
accordance with the present inventive subject matter, without concern as
to the frequency of the voltage from the power source and/or the voltage
level of the power source. To illustrate, skilled artisans are familiar
with a variety of situations in which the frequency of the line voltage
is 50 Hz, 60 Hz, 100 Hz or other values (e.g., if connected to a
generator, etc.) and/or in which the line voltage can change or vary, and
the problems that can be caused, particularly with conventional dimmers,
when connecting a light or set of lights to such line voltage. With
circuitry as described herein, a light or set of lights can be connected
to line voltages of widely differing frequencies and/or which vary in
voltage level, with good results.

[0088]In addition, the present inventive subject matter has been described
with regard to dimming, but the present inventive subject matter is also
applicable to modifying other aspects of the light output, e.g., color
temperature, color, hue, brightness, characteristics of the outputs of
the light, CRI Ra, etc. For example, a lighting control circuit can be
configured such that when the duty cycle of the input voltage is a
certain percentage (e.g., 10%), the circuitry can cause the output of the
device to have a particular color temperature (e.g., 2,000 K). For
instance, with natural light, as the light dims, the color temperature
typically decreases, and it might be deemed desirable for the lighting
device to mimic this behavior. In addition, with security lighting, it
can be desirable for dimmed lighting to have low CRI, such that there is
enough light that an intruder can be observed, but the CRI Ra is low
enough that the intruder has difficulty seeing what he or she is doing.

[0089]The circuits and methods according to the present inventive subject
matter are not limited to AC power or to AC phase cut dimmers. Rather,
the present inventive subject matter is applicable to all types of
dimming using waveform duty cycle (e.g., including pulse width
modulation).

[0090]While embodiments of the present inventive subject matter have been
described with reference to a circuit capable of being used with three
different types of dimming control, the present inventive subject matter
also includes circuits that may be used with any two of the different
dimming control techniques. Thus, a dimming signal generation circuit may
be capable of operation with more than one type of dimming control
signal. However, the circuit need only be capable of operation with one
type of dimming control signal at a time to still benefit from teachings
of the present inventive subject matter. For example, the same or
substantially the same dimming signal generation circuit could be
provided in a luminaire and the user would connect only one type of
dimming control device to the luminaire. Thus, the luminaire would be
compatible with multiple dimming control methods but would only be used
with one at a time.

[0091]Furthermore, benefits of the present inventive subject matter may
also be obtained even in cases where the luminaire is preconfigured to be
compatible with only one dimming solution. In such a case, the same basic
circuit topology could be utilized for various dimming control methods
and jumpers or changes in passive components could be utilized to tailor
the circuit for the desired dimming solution. Such a system may provide
advantages in manufacturing as common parts between the different systems
could be purchased based on total unit production. Furthermore, partial
circuits could be assembled and inventoried and then tailored to the
specific dimming method at final manufacturing time. This could reduce
the number of intermediate components that would need to be inventoried
during the production process.

[0092]While certain embodiments of the present inventive subject matter
have been illustrated with reference to specific combinations of
elements, various other combinations may also be provided without
departing from the teachings of the present inventive subject matter.
Thus, the present inventive subject matter should not be construed as
being limited to the particular exemplary embodiments described herein
and illustrated in the Figures, but may also encompass combinations of
elements of the various illustrated embodiments.

[0093]Many alterations and modifications may be made by those having
ordinary skill in the art, given the benefit of the present disclosure,
without departing from the spirit and scope of the inventive subject
matter. Therefore, it must be understood that the illustrated embodiments
have been set forth only for the purposes of example, and that it should
not be taken as limiting the inventive subject matter as defined by the
following claims. The following claims are, therefore, to be read to
include not only the combination of elements which are literally set
forth but all equivalent elements for performing substantially the same
function in substantially the same way to obtain substantially the same
result. The claims are thus to be understood to include what is
specifically illustrated and described above, what is conceptually
equivalent, and also what incorporates the essential idea of the
inventive subject matter.

[0094]Any two or more structural parts of the devices described herein can
be integrated. Any structural part of the devices described herein can be
provided in two or more parts (which are held together, if necessary).
Similarly, any two or more functions can be conducted simultaneously,
and/or any function can be conducted in a series of steps.